Unlike other rare earth elements, scandium due to its extremely small ion radius is rarely present in common rare earth minerals, but widely present in minor amounts in oxide minerals of aluminum, tin, tungsten, zirconium, iron, nickel, etc.
Since scandium has a low basicity due to the small ion radius, a strong acid is needed for its dissolution. When oxide minerals are dissolved with acid, many other elements are dissolved at the same time and coexist with scandium in the aqueous solution. Since the aqueous solution contains the main metal component from the oxide mineral in a high concentration, it is not easy to separate scandium from the aqueous solution.
One typical method known for scandium separation is solvent extraction using an acidic alkyl phosphate extractant such as PC-88A (Daihachi Chemical Industry Co., Ltd., main component: 2-ethylhexyl 2-ethylhexylphosphonate). Since PC-88A has an extremely high scandium trapping ability, back extraction is very difficult. Another method uses a carboxylic acid extractant, typically Versatic 10. In this case, extraction equilibrium is reached at or above pH 4, at which scandium hydroxide forms and interferes with extraction. Accordingly, there is a need for a method which can separate scandium efficiently.